Freeing goldfish in the Manning River an environmental concern

The one that didn't get away: Dr Stephen Beatty from the school of Veterinary and Life Sciences at Murdoch University in WA. with a goldfish caught in the river. Photo: associate professor David Morgan, Centre for Fish and Fisheries Research, Murdoch University.

Some people flush their unwanted pet goldfish down the toilet.

Some more sensitive people ‘set them free’ in local waterways.

Either way, neither is a good choice, for the fish or for the environment.

Feral goldfish are becoming a world wide problem and they are upsetting local ecosystems.

“There are emerging stories of goldfish populations burgeoning in the US and Canada and one clear message is that it is very difficult to get rid of them,” aquatic ecologist Dr Keith Bishop said.

They are very hardy species and that makes them very difficult to kill. Once a population is established, it is very hard to get rid of.

Goldfish can cause algal bloom in waterways as they disturb the river bottom which releases nutrients. They compete for food sources with native fish, and introduce parasites and potential diseases to the native fish population. All of these things put the local ecology out of balance.

Researchers from Murdoch University in Perth, WA have been working on a control program for the goldfish in the Vasse River, Busselton for 12 years, where they are having a problem with giant goldfish. The largest one they have found weighed 1.9 kilograms.

In our local river systems, Dr Bishop found an unsettling increase in goldfish numbers in his August 2016 survey.

What is worrying Dr Bishop is that he is also seeing an increase in distribution. In a survey he did last May, he noted a push upstream for the first time, and also a flood-assisted push downstream of juveniles.

“No doubt they will be showing up at Wingham now,” he said.

While Dr Bishop says the goldfish are “perhaps not a significant problem right now” for the Manning River, he is asking what the future will bring.